A variety of packers are used in wellbores to isolate specific wellbore regions. A packer is delivered downhole on a conveyance and expanded against the surrounding wellbore wall to isolate a region of the wellbore. Once set against the surrounding wellbore wall, the packer can be subjected to substantial heat, pressures and forces. Consequently, the packer may experience wear that increases the likelihood of packer failure.
The packer may be designed with metal cables extending between packer extremities, such as mechanical end fittings. The metal cables are surrounded with a rubber material that expands when the packer is expanded. During expansion, the spacing between each cable is increased and the rubber thickness is decreased. Under high differential pressures, high packer inflation pressures, and/or high temperatures, the rubber material can become viscous and creep. The movement of the rubber material may result in contact between cable layers and/or contact between cables and portions of the packer extremities. The contact between cables and the significant tension placed on the cables can lead to cable deterioration and breakage, ultimately ending in packer destruction. The damage often occurs at contact points between cables and an outer skirt of the packer extremity and/or at contact points between adjacent cables, often in proximity to one or both packer extremities. The cables tend to break at the side of the packer experiencing higher pressure differentials.
Packers also can experience undue wear and potential failure due to the presence of voids in the packer structure. The presence of voids potentially leads to detrimental collapse of the rubber material and/or friction between packer components during packer expansion. Additionally, the outer rubber layer of packers is susceptible to breakage at locations experiencing high axial pressure differentials. Breakage of the outer rubber layer typically occurs near the low-pressure end of the packer. Once breakage occurs, the broken rubber creates difficulties in extracting the packer. Also, breakage of the outer rubber layer tends to leave a gap between the packer and the wellbore, and the rubber material tends to expand to fill this gap. Consequently, as the packer expands, components of the mechanical structure, e.g. steel cables and anti-extrusion layers, can contact each other and create friction that leads to further damage of the packer.